arm64: dts: freescale: align watchdog node name with dtschema

The dtschema expects watchdog device node name to be "watchdog":

  arch/arm64/boot/dts/freescale/fsl-ls1012a-frdm.dt.yaml: wdog@2ad0000:
    $nodename:0: 'wdog@2ad0000' does not match '^watchdog(@.*|-[0-9a-f])?$'

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>